US20220073772A1 - Water-based inkjet yellow ink, ink set, and method for producing printed matter - Google Patents

Water-based inkjet yellow ink, ink set, and method for producing printed matter Download PDF

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Publication number
US20220073772A1
US20220073772A1 US17/414,500 US201917414500A US2022073772A1 US 20220073772 A1 US20220073772 A1 US 20220073772A1 US 201917414500 A US201917414500 A US 201917414500A US 2022073772 A1 US2022073772 A1 US 2022073772A1
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Prior art keywords
ink
pigment
yellow
water
mass
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US17/414,500
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English (en)
Inventor
Atsushi Yoda
Kazuhiro Jonai
Norio Suzuki
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Toyocolor Co Ltd
Artience Co Ltd
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Toyo Ink SC Holdings Co Ltd
Toyocolor Co Ltd
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Assigned to TOYO INK SC HOLDINGS CO., LTD., TOYOCOLOR CO., LTD. reassignment TOYO INK SC HOLDINGS CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: JONAI, KAZUHIRO, SUZUKI, NORIO, YODA, ATSUSHI
Publication of US20220073772A1 publication Critical patent/US20220073772A1/en
Assigned to ARTIENCE CO., LTD. reassignment ARTIENCE CO., LTD. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: TOYO INK SC HOLDINGS CO., LTD
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/38—Inkjet printing inks characterised by non-macromolecular additives other than solvents, pigments or dyes
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/40—Ink-sets specially adapted for multi-colour inkjet printing
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
    • C09B29/00—Monoazo dyes prepared by diazotising and coupling
    • C09B29/10—Monoazo dyes prepared by diazotising and coupling from coupling components containing hydroxy as the only directing group
    • C09B29/18—Monoazo dyes prepared by diazotising and coupling from coupling components containing hydroxy as the only directing group ortho-Hydroxy carbonamides
    • C09B29/20—Monoazo dyes prepared by diazotising and coupling from coupling components containing hydroxy as the only directing group ortho-Hydroxy carbonamides of the naphthalene series
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09B—ORGANIC DYES OR CLOSELY-RELATED COMPOUNDS FOR PRODUCING DYES, e.g. PIGMENTS; MORDANTS; LAKES
    • C09B57/00—Other synthetic dyes of known constitution
    • C09B57/04—Isoindoline dyes
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/03—Printing inks characterised by features other than the chemical nature of the binder
    • C09D11/033—Printing inks characterised by features other than the chemical nature of the binder characterised by the solvent
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/03—Printing inks characterised by features other than the chemical nature of the binder
    • C09D11/037—Printing inks characterised by features other than the chemical nature of the binder characterised by the pigment
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/02—Printing inks
    • C09D11/10—Printing inks based on artificial resins
    • C09D11/106—Printing inks based on artificial resins containing macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • C09D11/107—Printing inks based on artificial resins containing macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds from unsaturated acids or derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D11/00—Inks
    • C09D11/30—Inkjet printing inks
    • C09D11/32—Inkjet printing inks characterised by colouring agents
    • C09D11/322—Pigment inks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/0023—Digital printing methods characterised by the inks used

Definitions

  • Embodiments of the present invention relate to a water-based inkjet yellow ink, an ink set containing the yellow ink, and a method for producing a printed matter.
  • Inkjet printing systems are systems in which minute droplets of inks are ejected and landed from inkjet heads onto a recording medium to form images and/or text on the recording medium, and do not require a printing plate.
  • electrophotographic systems which are other printing systems that do not require a printing plate
  • the inkjet printing systems are superior in terms to the price of the apparatus itself, running cost during printing, apparatus size, high-speed printing characteristics, and the like. With the spread of digital printing and the expansion of applications, the inkjet printing system is expected to grow in the future.
  • the inks used in the inkjet printing system include a wide variety of types such as an oil type, a solvent type, an active energy ray-curable type, and an aqueous type.
  • the active energy ray-curable type inkjet printing system is becoming widespread because of the advantages that the systems are applicable not only to a paper substrate, but also to a non-absorption substrate such as plastic or glass, the system has excellent durability of the printed matter, and the system can realize high-speed printing.
  • restrictions on the use of solvents and monomers have been promoted from the viewpoint of consideration and countermeasures for harm to the environment and humans, and replacement with a water-based ink has been desired, and demand for a water-based ink is increasing.
  • the inkjet printing system will be developed in the existing printing market which adopts printing systems using a plate such as an offset printing system.
  • the productivity and color reproducibility of a recorded matter are very important.
  • many special color inks are used in the conventional offset printing system, and a printed matter with an excellent color reproduction region is produced, and therefore, in order to achieve practical use of the inkjet printing system in the existing printing market, it is important to realize excellent color reproducibility.
  • the printed matter obtained is not discolored or faded during storage, and also that the inkjet ink stored for a long period of time is required to have the same color reproducibility as in the initial stage.
  • the color reproduction region greatly changes depending on the degree of color reproduction potential of the colorants used, particularly the three colors of yellow, cyan, and magenta, which are process colors.
  • the colorants used particularly the three colors of yellow, cyan, and magenta, which are process colors.
  • Patent Literature 1 it is possible to use special color inks in order to improve color reproducibility, but it can be said that this is not a preferable measure from the viewpoint of reducing the cost and size of inkjet printers. Therefore, the selection of the above three color pigments is very important.
  • Patent Literatures 2 and 3 C. I. Pigment Yellow 180 and 213 are used as the yellow pigment.
  • the yellow ink using these pigments has a weak coloring power, and it is difficult to obtain a printed matter with excellent color reproducibility.
  • Patent Literature 3 although it is possible to improve the color reproducibility to some extent by increasing the pigment concentration in the yellow ink, the increase in the pigment concentration adversely affects the storage stability and the dispersion stability. In addition, it is easily presumed that inkjet printing stability over a long period of time will deteriorate.
  • the red color is formed by overlayering a yellow color and a magenta color, and therefore, in order to meet the various demands described above and to improve the color reproducibility of the red region, it is essential to improve the color reproducibility and image density of the yellow ink as the base.
  • An object of the present invention is to provide a water-based inkjet yellow ink with excellent color reproducibility and light resistance that can obtain a printed matter which does not cause discoloration and fading over time, and is also excellent in storage stability and dispersion stability.
  • Another object of the present invention is to provide a water-based inkjet yellow ink that can obtain a printed matter also with excellent image density in addition to the above.
  • Still another object of the present invention is to provide an ink set containing a water-based inkjet yellow ink and a water-based inkjet magenta ink that can obtain a printed matter with excellent balance of color reproducibility and light resistance in a red region, and a method for producing a printed matter using the ink set.
  • another object of the present invention is to provide an ink set containing a water-based inkjet yellow ink, a water-based inkjet magenta ink, and a water-based inkjet cyan ink or a water-based inkjet violet ink that can obtain a printed matter with excellent color reproducibility in a red region and a green region, and a method for producing a printed matter using the ink set.
  • the present inventors have recently found that the above objects can be achieved by using the combination of a yellow pigment with a specific structure and a basic organic compound with a specific pKa value as an water-based inkjet yellow ink in a color inkjet printing system, and further by defining a boiling point of an organic solvent contained in the ink. Furthermore, it has been found that a printed matter in which high color rendering in a red region is particularly achieved can be obtained by using the water-based inkjet yellow ink described above in combination with a water-based inkjet magenta ink.
  • a printed matter in which high color rendering in a red region and a green region is particularly achieved can be obtained by using the water-based inkjet yellow ink described above in combination with a water-based inkjet magenta ink and a specific water-based inkjet cyan ink or a specific water-based inkjet violet ink.
  • one embodiment of the present invention relates to a water-based inkjet yellow ink containing a yellow pigment (A) having a partial structure represented by general formula (1), an organic solvent, a basic organic compound, and water, wherein
  • an amount of the yellow pigment (A) is 1 to 10% by mass of a total mass of the water-based inkjet yellow ink;
  • the basic organic compound contains 0.1 to 1.25% by mass of a basic organic compound (B) having a pKa value of 9.5 or less at 25° C. of the total mass of the water-based inkjet yellow ink, and
  • general formula (1) has at least one bonding site
  • X 1 and X 2 represent both ⁇ O or both ⁇ CR 6 R 7 , or X 1 is ⁇ O and X 2 is ⁇ NR 8 ,
  • each R 1 to R 4 independently represents a hydrogen atom or a halogen atom
  • R 1 represents a hydrogen atom or a bonding site
  • each R 6 to R 8 represents a bonding site.
  • one embodiment of the present invention relates to the water-based inkjet yellow ink described above, wherein an amount of the basic organic compound (B) having a pKa value of 9.5 or less at 25° C. is 0.1 to 1% by mass of the total mass of the water-based inkjet yellow ink.
  • one embodiment of the present invention relates to any one of the water-based inkjet yellow inks described above, wherein the yellow pigment (A) includes C. I. Pigment Yellow 139 and/or C. I. Pigment Yellow 185.
  • one embodiment of the present invention relates to any one of the water-based inkjet yellow inks described above, wherein an amount of impurities contained in the yellow pigment (A) is 5% by mass or less of a total mass of the yellow pigment (A).
  • one embodiment of the present invention relates to an inkjet ink set containing:
  • a water-based inkjet magenta ink containing a magenta pigment and water.
  • one embodiment of the present invention relates to the inkjet ink set described above, wherein
  • the water-based inkjet magenta ink contains 1 to 10% by mass of a magenta pigment having a partial structure represented by general formula (2) shown below of a total mass of the water-based inkjet magenta ink, General formula (2):
  • each R 9 , R 10 , and R 11 is independently any one of a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an anilide group, a carbamoyl group, a methoxycarbonyl group, an ethoxycarbonyl group, and a sulfonamide group, and
  • R 12 is any one of a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, and a structure represented by general formula (3) shown below,
  • R 13 represents a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an amino group, or a nitro group,
  • each R 14 and R 15 independently represents a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an amino group, or a nitro group, or R 14 and R 15 are bonded to each other to form an imidazolidinone ring,
  • the structure represented by general formula (3) is bonded to a nitrogen atom in the partial structure represented by general formula (2) at a position of “*”.
  • one embodiment of the present invention relates to any one of the inkjet ink sets described above, wherein
  • the magenta pigment having a partial structure represented by general formula (2) includes at least one selected from the group consisting of C. I. Pigment Red 146, C. I. Pigment Red 147, C. I. Pigment Red 150, C. I. Pigment Red 185, C. I. Pigment Red 266, and C. I. Pigment Red 269.
  • one embodiment of the present invention relates to any one of the inkjet ink sets described above, further comprising a water-based inkjet cyan ink, wherein
  • the water-based inkjet cyan ink includes at least one selected from the group consisting of C. I. Pigment Blue 15:3 and C. I. Pigment Blue 15:6.
  • one embodiment of the present invention relates to any one of the inkjet ink sets described above, further containing a water-based inkjet violet ink, wherein
  • the water-based inkjet violet ink includes at least one selected from the group consisting of C. I. Pigment Violet 3, C. I. Pigment Violet 23, C. I. Pigment Violet 27, and C. I. Pigment Violet 32.
  • one embodiment of the present invention relates to an inkjet ink set which contains any one of the water-based inkjet yellow inks described above, a water-based inkjet magenta ink, and a water-based inkjet cyan ink, and does not contain other water-based inkjet chromatic ink.
  • one embodiment of the present invention relates to an inkjet ink set which contains any one of the water-based inkjet yellow inks described above, a water-based inkjet magenta ink, and a water-based inkjet violet ink, and does not contain other water-based inkjet chromatic ink.
  • one embodiment of the present invention relates to an inkjet ink set which contains any one of the water-based inkjet yellow inks described above, a water-based inkjet magenta ink, a water-based inkjet cyan ink, and a water-based inkjet violet ink, and does not contain other water-based inkjet chromatic ink.
  • one embodiment of the present invention relates to a method for producing a printed matter including printing any one of the water-based inkjet yellow inks described above or any one of the inkjet ink sets described above on a recording medium using an inkjet printing system.
  • One embodiment of the present invention is able to provide a water-based inkjet yellow ink with excellent color reproducibility and light resistance that can obtain a printed matter which does not cause discoloration and fading over time, and is also excellent in storage stability and dispersion stability.
  • Another embodiment of the present invention is able to provide a water-based inkjet yellow ink that can obtain a printed matter also with excellent image density in addition to the above.
  • Still another embodiment of the present invention is able to provide an ink set containing a water-based inkjet yellow ink and a water-based inkjet magenta ink that can obtain a printed matter with an excellent balance of color reproducibility and light resistance in a red region, and a method for producing a printed matter using the ink set.
  • another embodiment of the present invention is able to provide an ink set containing a water-based inkjet yellow ink, a water-based inkjet magenta ink, and a water-based inkjet cyan ink or a water-based inkjet violet ink that can obtain a printed matter with excellent color reproducibility in a red region and a green region, and a method for producing a printed matter using the ink set.
  • the yellow ink according to an embodiment of the present invention contains 1 to 10% by mass of a yellow pigment (A) having a partial structure represented by general formula (1) of the total mass of the yellow ink, and 0.1 to 1.25% by mass of a basic organic compound (B) having a pKa value of 9.5 or less at 25° C. of the total mass of the yellow ink. Further, the amount of an organic solvent having a boiling point of 240° C. or higher under 1 atmosphere is 5% by mass or less (may be 0% by mass) of the total mass of the yellow ink.
  • aqueous medium means a medium composed of a liquid containing at least water.
  • a certain amount of a yellow pigment having a specific partial structure is used together with a basic organic compound having a specific pKa value, and the boiling point of an organic solvent to be used together is specified to achieve both of the above characteristics.
  • the yellow ink contains 1 to 10% by mass of a yellow pigment (A) having a partial structure represented by general formula (1) shown below of the total mass of the yellow ink.
  • General formula (1) has at least one bonding site.
  • X 1 and X 2 represent both ⁇ O or both ⁇ CR 6 R 7 , or X 1 is ⁇ O and X 2 is ⁇ NR 8 .
  • Each R 1 to R 4 independently represents a hydrogen atom or a halogen atom
  • R 5 represents a hydrogen atom or a bonding site
  • each R 6 to R 8 represents a bonding site.
  • the partial structure represented by general formula (1) includes phthalimide (in general formula (1), X 1 and X 2 are both ⁇ O. Examples include C. I. Pigment Yellow 138), isoindolinone (In general formula (1), X 1 is ⁇ O and X 2 is ⁇ NR 8 . Examples include C. I. Pigment Yellow 109 and 100) isoindoline (n general formula (1) X 1 and X 2 are both ⁇ CR 6 R 7 . Examples include C. I. Pigment Yellow 139 and 185), and the like.
  • the yellow ink may contain only one type of the above pigments, or may contain two or more types in combination. If two or more types are used in combination, those in a mixed crystal state may be used.
  • C. I. Pigment Yellow 139 and 185 known as an isoindoline-based yellow pigment are preferably selected.
  • the amount of impurities present in the yellow pigment (A) is preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass, of the total mass of the yellow pigment (A).
  • the amount of impurities may be 0% by mass.
  • the amount of impurities in the yellow pigment (A) can be measured by using the method described in examples below.
  • an alkali metal ion and an alkaline earth metal ion such as a sodium ion and a calcium ion
  • an alkali metal ion and an alkaline earth metal ion are rapidly dissolved (ionized) in an aqueous medium and can move and diffuse arbitrarily, and accordingly, blockages of inkjet head nozzles may be caused at the time of discharge in addition to the inhibition of adsorption described above. Therefore, it is preferable to reduce the amount of a sodium ion and a calcium ion as much as possible.
  • the amount of a sodium ion and the amount of a calcium ion contained in the yellow pigment (A) are preferably 80 ppm or less (may be 0 ppm), more preferably 50 ppm or less (may be 0 ppm), and still more preferably 20 ppm or less (may be 0 ppm), respectively.
  • a method for reducing impurities present in the yellow pigment (A) there is a method of washing the synthesized yellow pigment (A) with water and/or an organic solvent. In particular, it is preferable to perform one or more times of each of the washing process using water and the washing process using an organic solvent.
  • a pure water or an ion exchanged water is preferably used as water.
  • the total amount of the yellow pigment (A) contained in the yellow ink is 1 to 10% by mass, and more preferably is 1.5 to 9.5% by mass of the total mass of the yellow ink.
  • the total amount of the yellow pigment (A) is particularly preferably 2 to 8% by mass, and most preferably 3 to 5.5% by mass.
  • the yellow ink contains a basic organic compound.
  • the basic organic compound contains 0.1 to 1.25% by mass of a basic organic compound (B) having a pKa value of 9.5 or less at 25° C. and preferably 0.1 to 1.0% by mass, of the total mass of the yellow ink.
  • the basic organic compound may include a basic organic compound having a pKa value of more than 9.5.
  • the dispersed state of the pigment is maintained due to the charge repulsion generated between the pigment particles, and storage stability and dispersion stability are ensured.
  • the yellow pigment (A) described above is known to have weak durability to basic materials.
  • the yellow pigment (A) in the printed matter may decompose over time, and there is a possibility that discoloration and/or fading are caused.
  • the pKa value of the basic organic compound (B) is preferably 8.5 or less.
  • the lower limit of the pKa value of the basic organic compound (B) is not particularly limited.
  • the pKa value is 3 or more, preferably 4.5 or more, and more preferably 6.5 or more.
  • the basic organic compound (B) preferably contains an aminoalcohol (alkanolamine), and particularly preferably contains triethanolamine which has a small pKa value. Only one of the above compounds may be used, or alternatively two or more of them may be used in combination. Examples of the case where two or more types are used in combination include a basic organic compound (B) containing a basic organic compound having a pKa value of 8.5 or less and a basic organic compound having a pKa value of more than 8.5; and a basic organic compound (B) containing triethanolamine and a basic organic compound other than triethanolamine, and the like.
  • pKa can be measured using a known method, for example, a potentiometric titration method using water as the solvent in a 25° C. environment by using an automatic potentiometric titrator AT-710S manufactured by Kyoto Electronics Manufacturing Co., Ltd.
  • the molecular weight of the basic organic compound (B) contained in the yellow ink is preferably 500 or less, more preferably 300 or less, and particularly preferably 200 or less. Further, the molecular weight is preferably 50 or more, more preferably 75 or more, and particularly preferably 100 or more.
  • the basic organic compound (B) having the molecular weight described above By using the basic organic compound (B) having the molecular weight described above, overdrying and remaining of the basic organic compound (B) at the time of printing can be prevented, and an ink with excellent color reproducibility and drying properties of the printed matter can be obtained. Further, although details are unclear, the basic organic compound (B) having the above molecular weight causes little damage to the yellow pigment (A), and can improve the storage stability and dispersion stability of the ink.
  • the amount of the basic organic compound (B) in the yellow ink is 0.1 to 1.25% by mass of the total mass of the yellow ink. If the amount is 0.1% by mass or more, it is easy to ensure storage stability for a long period of time, and the dispersion state of the yellow pigment (A) is not destroyed even when water is volatilized on inkjet head nozzles, and accordingly the deterioration in the quality of the printed matter due to the occurrence of blockages of nozzles or the like can be prevented. By adding 1.25% by mass or less, it is possible to prevent fading and discoloration of the printed matter over time.
  • the amount of the basic organic compound (B) is preferably 0.1 to 1.0% by mass of the total mass of the yellow ink.
  • any optional component such as a pH adjuster and/or a surfactant described below is also included in the basic organic compound (B), if they correspond to the basic organic compound satisfying the pKa described above.
  • the yellow ink contains a “pigment dispersing resin and/or binder resin” having an acid group as an optional component, and a “pigment dispersing resin and/or binder resin” having an acid group neutralized with a basic organic compound satisfying the pKa described above is used as the “pigment dispersing resin and/or binder resin” having an acid group
  • the basic organic compound (hereinafter referred to as a “basic organic compound (b2)”) satisfying the pKa described above used for neutralization is also included in the basic organic compound (B).
  • the basic organic compound (b2) forms intermolecular interaction with the “pigment dispersing resin and/or binder resin” having an acid group. Therefore, in some embodiments, the amount obtained by subtracting the amount of the basic organic compound (b2) from the total amount of the basic organic compound (B) contained in the yellow ink is preferably 0.1 to 1.0% by mass.
  • the basic organic compound (B) other than the basic organic compound (b2) may be referred to as a basic organic compound (b1).
  • the basic organic compound (b1) and the basic organic compound (b2) may be the same compound or compounds different from each other. If they are the same compound, the basic organic compound (b1) and the basic organic compound (b2) are preferably an amino alcohol (alkanolamine), and more preferably triethanolamine. If the compounds are different compounds, the combinations of the basic organic compound (b1) and the basic organic compound (b2) include, for example, a basic organic compound having a pKa value of 8.5 or less and a basic organic compound having a pKa of more than 8.5; and triethanolamine and a basic organic compound other than triethanolamine.
  • the basic organic compound may contain a basic organic compound having a pKa value of more than 9.5. If the basic organic compound contains the basic organic compound having a pKa value of more than 9.5, the amount of the basic organic compound having a pKa value of more than 9.5 is preferably more than 0% by mass but not more than 0.5% by mass, and more preferably more than 0% by mass but not more than 0.25% by mass, of the total mass of the yellow ink.
  • the total amount of the basic organic compound (the total amount of the basic organic compound (B) and the basic organic compound having a pKa value of more than 9.5) is preferably 0.1 to 2.0% by mass, more preferably 0.1 to 1.5% by mass, and still more preferably 0.1 to 1.25% by mass, of the total mass of the yellow ink.
  • Specific examples include a yellow ink in which the amount of the basic organic compound (B) is 0.1 to 1.0% by mass of the total mass of the yellow ink, and the total amount of the basic organic compounds (the total amount of the basic organic compound (B) and the basic organic compound having a pKa value of more than 9.5) is 1.5% by mass or less of the total mass of the yellow ink.
  • the amount of an organic solvent having a boiling point of 240° C. or higher at 1 atmosphere (hereinafter, also referred to as a “high boiling point organic solvent”) is 5% by mass or less of the total mass of the yellow ink (may be 0% by mass).
  • the high boiling point organic solvent tends to remain in the printed matter subjected to printing.
  • the high boiling point organic solvent since the high boiling point organic solvent has high hygroscopicity, if the printed matter is stored for a long period of time, the high boiling point organic solvent may absorb moisture in the atmosphere. If the boiling point of the basic organic compound (B) to be used is high, it is considered that a part of the basic organic compound (B) also remains in the printed matter. In this case, it is also considered that the basic organic compound (B) is eluted into water absorbed by the high boiling point organic solvent and diffuses into the printed matter, thereby damaging the yellow pigment (A).
  • the printed matter produced by using an ink containing an excessive amount of the high boiling point organic solvent may cause fading and discoloration over time. Therefore, in an embodiment of the present invention, the phenomenon described above is suppressed by ensuring the amount of the high boiling point organic solvent in the yellow ink of a certain amount or less.
  • the amount of the high boiling point organic solvent is preferably small, for example, more preferably 3% by mass or less, and particularly preferably 1.5% by mass or less, of the total mass of the yellow ink.
  • the boiling point at 1 atmosphere can be measured by using a thermal analysis device such as DSC (Differential Scanning Calorimetry).
  • the organic solvent is preferably a water-soluble organic solvent.
  • an organic solvent having a surface tension at 25° C. of 20 to 35 mN/m can be preferably used. This is because the static surface tension of the yellow ink can be reduced and the wettability and permeability to the recording medium are improved, so that a printed matter with excellent image density, color reproducibility, and other image quality can be obtained, and the drying properties of the ink can also be improved.
  • the surface tension is described in “Chemical Handbook, Basic Edition, Revised 5th Edition” (Maruzen Publishing Co., Ltd., 2004) edited by the Chemical Society of Japan, and can be referred to. Further, the surface tension can be measured by the Wilhelmy method (plate method, vertical plate method) using a CBVP-Z surface tension meter manufactured by Kyowa Interface Science Co., Ltd.
  • the viscosity of the water-soluble organic solvent at 25° C. is preferably 1 to 20 mPa ⁇ s.
  • the viscosity can be measured by, for example, TVE-25L (cone plate type E-type viscometer) manufactured by Toki Sangyo Co., Ltd.
  • Aliphatic polyols are preferably used as the solvent having the above characteristics. Among them, those having a boiling point at 1 atmosphere of 180° C. or more but 250° C. or less are preferably selected, and those having a boiling point of 180° C. or more but less than 240° C. are more preferably selected. This is because by using an aliphatic polyol that satisfies the above boiling point range, it is possible to easily control the wettability, permeability, and drying properties of the yellow ink without being affected by the type of the recording medium. In addition, this provides images with excellent image density, color reproducibility, and other image quality for various recording media without increasing the size of the drying device while maintaining the moisture retention on inkjet head nozzles.
  • the boiling point at 1 atmosphere can be measured by using, for example, a thermal analysis device.
  • the surfactant described below is not included in the aliphatic polyols.
  • the aliphatic polyol having a boiling point of 180 to 250° C. is not limited to the following, but for example, 1,2-propanediol (propylene glycol, boiling point: 188° C.), 1,2-butanediol (boiling point: 194° C.), 1,2-ethandiol (ethylene glycol, boiling point: 197° C.), 2-methylpentane-2,4-diol (boiling point: 197° C.), 3-methyl-1,3-butanediol (boiling point: 203° C.), 1,3-butanediol (butylene glycol, boiling point: 207° C.), 1,2-pentanediol (boiling point: 210° C.), 1,3-propanediol (boiling point: 210° C.), 2,2-dimethyl-1,3-propanediol (boiling point: 210° C.),
  • the yellow ink contains two or more types of the aliphatic polyols described above, and the total amount of the aliphatic polyols is in the range from 10 to 30% by mass of the total mass of the yellow ink.
  • the wettability, permeability, and drying properties of the recording medium can be easily controlled.
  • a printed matter with excellent image density, color reproducibility, and other image quality can be obtained for both of a substrate having an absorbing layer and a low-absorption substrate.
  • At least one type of the two or more types of aliphatic polyols contained is preferably an alkanediol, and all of the aliphatic polyols contained in the yellow ink are more preferably an alkanediol.
  • a highly hydrophobic low-penetration substrate such as a coated paper, an art paper, or a polyvinyl chloride sheet, which are generally cited as a recording medium used for a printed matter for industrial applications, and a printed matter with excellent image density, color reproducibility, and other image quality can be obtained with respect to the substrates described above.
  • At least one selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-ethanediol, 1,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol is preferably used from the viewpoint of moisture retention and drying properties.
  • these solvents are preferably selected from the viewpoint that they do not adversely affect the dispersion state of the yellow pigment (A), and as a result, the storage stability of the yellow ink can be improved.
  • the yellow ink containing two or more selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol as the water-soluble organic solvent, in which the total amount of the two or more water-soluble organic solvents is 10 to 30% by mass of the total mass of the yellow ink is most preferable.
  • a yellow ink satisfying the above conditions can obtain a printed matter which has excellent image density, color reproducibility, and other image quality regardless of the recording medium used, and also has excellent storage stability.
  • organic solvents may also be used in combination to adjust the moisture retention and penetration of the yellow ink to the recording medium.
  • examples of other organic solvent include glycol monoalkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monopentyl ether, diethylene glycol monohexyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol monomethyl ether; glycol dial
  • a pigment other than the yellow pigment (A) may be used in combination.
  • the amount of the yellow pigment (A) with respect to the total mass of the pigment used is preferably 50% by mass or more.
  • the amount of the yellow pigment (A) is more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more.
  • the amount of the yellow pigment (A) with respect to the total mass of the pigment used may be 100% by mass.
  • Examples of the pigment other than the yellow pigment (A) that can be used in an embodiment of the present invention include C. I. Pigment Yellow 1, 2, 3, 10, 11, 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 117, 120, 125, 128, 137, 147, 148, 150, 151, 154, 155, 166, 168, 180 and 213.
  • only one type of the above pigments may be used, or two or more types may be used in combination. If two or more types are used in combination, those in a mixed crystal state may be used. Further, if two or more types of pigments are not in a mixed crystal state, that is, two or more types of pigments each having a different crystal structure are used, the two or more types of pigments may be mixed and dispersed from the beginning by using the method described below or the like, or separately dispersed pigment dispersions may be mixed later.
  • the total amount of the pigment contained in the yellow ink is preferably 1 to 10% by mass, and more preferably 1.5 to 9.5% by mass of the total mass of the yellow ink.
  • examples of a method of stably dispersing and preserving a pigment in the inkjet ink include a method of dispersing a pigment by making a water-soluble resin adsorbed on the surface of the pigment; a method of dispersing a pigment by making a water-soluble and/or water-dispersible surfactant adsorbed on the surface of the pigment; a method of dispersing a pigment in an ink by chemically and/or physically introducing a hydrophilic functional group on the surface of the pigment without any dispersant and surfactant; and a method of coating a pigment with a water-insoluble resin to form microcapsules.
  • a method of dispersing with a resin (also referred to as a “pigment dispersing resin” in the present description) is preferable, and a method of dispersing with a water-soluble resin is more preferable.
  • a resin also referred to as a “pigment dispersing resin” in the present description
  • a method of dispersing with a water-soluble resin is more preferable. This is because by selecting and examining the composition and/or the molecular weight of monomers which form the resin, adsorbing ability of the resin to the pigment can be easily increased, and the dispersion stability can be imparted to the fine pigment, and accordingly a yellow ink with excellent color development and color reproducibility can be obtained.
  • the type of the pigment dispersing resin is not particularly limited, and examples thereof include a (meth)acrylic resin, a styrene (meth)acrylic resin, a maleic acid resin, a styrene maleic acid resin, an urethane resin, an ester resin, an amide resin, and an imide resin.
  • a (meth)acrylic resin, a styrene (meth)acrylic resin, an urethane resin, and an ester resin is preferable in terms of storage stability and dispersion stability of the yellow ink.
  • the structure of the resin is also not particularly limited, and examples thereof include a random structure, a block structure, a comb-shaped structure, or a star-shaped structure.
  • (meth)acrylic means acrylic or methacrylic.
  • an aromatic ring structure into the pigment dispersing resin because it is possible to improve the pigment dispersibility, the color reproducibility of the printed matter, and the storage stability and dispersion stability of the ink.
  • a functional group having an aromatic ring structure include a phenyl group, a naphthyl group, an anthryl group, a tolyl group, a xylyl group, a mesityl group, an anisyl group and the like, and a phenyl group, a naphthyl group or a tolyl group is preferable.
  • the reason is that the aromatic ring structure contained in the yellow pigment (A) and the aromatic ring structure contained in the pigment dispersing resin interact with each other to remarkably improve the adsorbing ability of the pigment dispersing resin to the yellow pigment (A), and even if the pigment is finely dispersed, the color reproducibility of the printed matter and the storage stability and dispersion stability of the ink can be ensured over a long period of time.
  • the compounding ratio of the monomer having the aromatic ring structure with respect to the total mass of the monomers used in resin synthesis is expressed by the compounding ratio of the monomer having the aromatic ring structure with respect to the total mass of the monomers used in resin synthesis, the compounding ratio is preferably 10% by mass or more but 70% by mass or less, and particularly preferably 15% by mass or more but 50% by mass or less. If the compounding ratio is 10% by mass or more, the adsorbing ability to the yellow pigment (A) can be improved, and as a result, it is possible to obtain a yellow ink with excellent color reproducibility, storage stability and dispersion stability of the printed matter. If the compounding ratio is 70% by mass or less, the viscosity of the pigment dispersion and the ink can be maintained within a range suitable for inkjet applications.
  • a pigment dispersing resin having an alkyl group having 10 to 36 carbon atoms from the viewpoint of storage stability and dispersion stability.
  • Examples of a method of synthesizing a pigment dispersing resin having an alkyl group include a method of condensing an alcohol and/or an amine having an alkyl group with a functional group such as a carboxylic acid within the resin skeleton of the base structure, a method of using a monomer having an alkyl group at the time of synthesis, or the like.
  • the alkyl group particularly preferably has 10 to 36 carbon atoms, and although both linear and branched can be used, a linear alkyl group is more preferable.
  • the linear alkyl group include a lauryl group (C12), a myristyl group (C14), a cetyl group (C16), a stearyl group (C18), an arachyl group (C20), a behenyl group (C22), a lignoceryl group (C24), cerotoyl group (C26), montanyl group (C28), melissyl group (C30), dotriacontanyl group (C32), tetratriacontanyl group (C34), and hexatriacontanyl group (C36).
  • the storage stability and dispersion stability of the pigment dispersion and the ink can be improved and also the viscosity of the pigment dispersion and the ink can be reduced.
  • the number of carbon atoms of the alkyl group is preferably 12 to 30, and still more preferably 18 to 24.
  • the acid value of the pigment dispersing resin is preferably 50 to 400 mgKOH/g.
  • the acid value of the pigment dispersing resin is preferably 100 to 350 mgKOH/g, and still more preferably 150 to 300 mgKOH/g.
  • the acid value of the resin in the present description is a value of mg of potassium hydroxide (KOH) required for neutralizing an acid contained in 1 g of the resin, and is a value titrated using a KOH solution in an ethanol/toluene mixed solvent.
  • the acid value can be measured, for example, by using the “automatic potentiometric titrator AT-610” manufactured by Kyoto Electronics Manufacturing Co., Ltd.
  • the weight average molecular weight of the pigment dispersing resin is preferably in the range from 1,000 to 100,000, and more preferably in the range from 5,000 to 50,000. If the molecular weight is in the range described above, the yellow pigment (A) is stably dispersed in water, and the viscosity is easily adjusted when applied to the yellow ink. If the weight average molecular weight is 1,000 or more, the pigment dispersing resin is less likely to dissolve in the organic solvent, and accordingly the resin adsorbed on the yellow pigment (A) is less likely to be desorbed, and as a result, the storage stability and dispersion stability are remarkably improved. In addition, by ensuring the weight average molecular weight of 100,000 or less, it is also possible to improve the discharge stability from inkjet heads.
  • the weight average molecular weight in the present description can be measured by using a conventional method. Specifically, it is obtained as a polystyrene-equivalent value measured using a TSK gel column (manufactured by Tosoh Corporation) and a GPC measuring apparatus (HLC-8120 GPC manufactured by Tosoh Corporation) equipped with an RI detector, and using THF as the eluent.
  • the acid group in the pigment dispersing resin is neutralized with a base in order to increase the solubility of the pigment dispersing resin in water.
  • a base an organic compound such as dimethylaminoethanol, diethanolamine and triethanolamine, and an inorganic compound such as ammonia, lithium hydroxide, sodium hydroxide and potassium hydroxide can be used.
  • Neutralization may be partial neutralization or complete neutralization.
  • the organic compound may be an organic compound corresponding to the basic organic compound (B) (that is, the basic organic compound (b2)) or an organic compound not corresponding to the basic organic compound (B) (that is, a basic organic compound having a pKa value of more than 9.5).
  • the basic organic compound (b2) is preferably, for example, a basic organic compound having a pKa of 8.5 or less.
  • the basic organic compound (b2) is preferably, for example, a basic organic compound having a pKa of more than 8.5.
  • the organic compound for neutralization is preferably a compound not corresponding to the basic organic compound (B) (that is, a basic organic compound having a pKa value of more than 9.5).
  • the amount of the pigment dispersing resin is preferably 1 to 50% by mass relative to the total mass of the pigment.
  • the amount ratio of the pigment dispersing resin is preferably 2 to 45% by mass, more preferably 4 to 40% by mass, and still more preferably 5 to 35% by mass, relative to the total mass of the pigment.
  • a pigment derivative can be used for the purpose of improving the adsorbability of the pigment dispersing resin to the yellow pigment (A) and the pigment other than the yellow pigment (A), improving the storage stability and dispersion stability of the pigment, achieving fine dispersion, and improving the color reproducibility of the printed matter.
  • a compound having an organic coloring material as the basic skeleton and having a substituent introduced into the molecule is preferable, and examples thereof include compounds represented by general formulas (4) to (6) shown below.
  • P is an n 1 -valent organic coloring material residue
  • n 1 is an integer of 1 or more
  • Z 1 represents a sulfonic acid group or a carboxyl group
  • n 1 is preferably 1 to 5, more preferably 1 to 3, still more preferably 1 to 2, and most preferably 1.
  • Z 1 is preferably a sulfonic acid group.
  • P is an n 2 -valent organic coloring material residue
  • n 2 is an integer of 1 or more
  • Z 2 represents SO 3 ⁇ or COO ⁇
  • Z 3 represents an alkali metal cation, NH 4 + , a primary ammonium cation, a secondary ammonium cation, a tertiary ammonium cation, or a quaternary ammonium cation
  • n 2 s are preferably 1 to 5, more preferably 1 to 3, still more preferably 1 to 2, and most preferably 1.
  • P is an n 3 -valent organic coloring material residue
  • n 3 is an integer of 1 or more
  • R 16 represents an organic group represented by general formula (7) shown below, n 3 is preferably 1 to 5, more preferably 1 to 3, still more preferably 1 to 2, and most preferably 1.
  • R 17 represents an (m+1)-valent organic residue
  • m represents an integer of 1 or more
  • R 18 s represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 10 carbon atoms.
  • R 18 s are preferably an alkylene group having 1 to 10 carbon atoms, and more preferably an alkylene group having 1 to 5 carbon atoms. It is preferable that R 18 s are all hydrogen atoms.
  • Examples of the organic coloring material residue (P) include an azo-based residue, a benzimidazolone-based residue, a phthalocyanine-based residue, a quinacridone-based residue, an anthraquinone-based residue, a dioxazine-based residue, a diketopyrrolopyrrole-based residue, a quinophthalone-based residue, an isoindolinone-based residue, an isoindoline-based residue, a perylene-based residue, a perinone-based residue, a flavanthrone-based residue, a pyranthrone-based residue, or an anthrapyrimidine-based residue.
  • the structure of the organic coloring material residue (P) does not necessarily need to be identical to the structure of the pigment, it is preferable to select one having a hue close to that of the ink. Further, it is preferable that the organic coloring material residue (P) has a structure similar to that of the pigment used for the ink. As a result, the adsorption with the pigment is enhanced, and the effect of improving the stability is easily exhibited.
  • the pigment derivative represented by general formula (6) described above has a structure similar to the partial structure of the yellow pigment (A) represented by general formula (1), the pigment derivative has a particularly high affinity with the yellow pigment (A) and is suitably selected.
  • the yellow pigment (A) can be fined and the particle size distribution can be narrowed by using the yellow pigment (A) in combination with a pigment dispersing resin having an aromatic ring structure.
  • the amount of coarse particles contained in the yellow ink is remarkably reduced, and accordingly the discharge stability from the inkjet heads can be improved, and the storage stability and the dispersion stability can also be improved.
  • a printed matter with excellent color reproducibility or the like can be obtained. Further, since the amount of coarse particles present on the surface of the printed matter is remarkably reduced and the smoothness of the surface is increased, it is possible to suppress irregular reflection of light incident on the printed matter. As a result, high density of the printed matter can be achieved.
  • the amount thereof is preferably 0.1 to 10% by mass, and particularly preferably 0.1 to 5% by mass, relative to the total mass of the pigment in the ink. If the amount is 0.1% by mass or more, the addition ratio to the pigment becomes sufficient, and the color reproducibility of the printed matter, and the storage stability and the dispersion stability are improved. If the amount is 10% by mass or less, the pigment is not fined unnecessarily, and accordingly the storage stability and dispersion stability can be improved and the deterioration in the light resistance of the printed matter can be prevented.
  • Examples of a method for producing the pigment dispersion include a following method, but are not limited thereto. First, a yellow pigment (A) and an optional component such as other pigment, a pigment derivative and an organic solvent are added to a solution containing a pigment dispersing resin, water, and an organic solvent as desired, mixed and stirred, and then are subjected to dispersion treatment using a dispersion device. Then, the pigment dispersion can be obtained by centrifugation and/or filtration as desired. Any known dispersion device can be used as the dispersion device, but a bead mill is preferably used.
  • the pigment preferably has an average secondary particle size (D50) of from 40 nm to 500 nm, more preferably from 50 nm to 400 nm, and particularly preferably from 60 nm to 300 nm, from the viewpoint of being able to obtain a printed matter with excellent image density and color reproducibility.
  • the average secondary particle size is, for example, a volume-based median size measured using a dynamic light scattering method. Specifically, the measurement can be performed using Nanotrac UPA-EX150 manufactured by MicrotracBEL Corporation, and using an ink diluted with water as desired.
  • Methods of adjusting the average secondary particle size include reducing the size of the pulverizing medium in the dispersion device, changing the material of the pulverizing medium, increasing the filling rate of the pulverizing medium, changing the shape of the agitating member (agitator), increasing the dispersion processing time, classifying with a filter and/or a centrifuge after the dispersion treatment, and combinations of these methods.
  • the size of the pulverizing medium of the dispersion device is preferably 0.1 to 3 mm. Further, glass, zircon, zirconia and titania are preferably used as a material of the pulverizing medium.
  • the yellow ink preferably contains a binder resin.
  • resin microparticles and a water-soluble resin are known as a binder resin for the water-based inkjet ink, and in an embodiment of the present invention, either one of them may be selected and used, or both of them may be used in combination.
  • Types of the resin used as the binder resin include a (meth)acrylic resin, a styrene (meth)acrylic resin, a maleic acid resin, a styrene maleic acid resin, a styrene butadiene resin, an urethane resin, an amide resin, an imide resin, and an olefin resin.
  • a (meth)acrylic resin, a styrene (meth)acrylic resin, an urethane resin, and an olefin resin are preferable, when the storage stability and dispersion stability of the yellow ink and the durability of the printed matter are taken into consideration.
  • the acid group in the binder resin may be neutralized with a base.
  • the description of the base used to neutralize the pigment dispersing resin can also be applied to the binder resin.
  • the resin microparticles are suitable for increasing the durability of the printed matter because the resin microparticles have a higher molecular weight than the water-soluble resin, or because the viscosity the ink can be lowered and a larger amount of the resin can be blended in the ink.
  • the resin microparticles in a dispersed state aggregate and form a film when the water volatilizes, and accordingly blockages of inkjet head nozzles are caused.
  • a printed matter is inferior in surface smoothness, and as a result, the image density and/or the color reproducibility may be lowered.
  • the monomer composition for obtaining the resin microparticles is controlled so that the glass transition point (Tg) is set to 80° C. or higher, the amount of the resin microparticles in the yellow ink is set to be 2% by mass or less, or both of them may be performed. From this point of view, when the resin microparticles are used, it is particularly preferable to select styrene (meth)acrylic resin microparticles and/or olefin resin microparticles.
  • the inventors of the present invention have studied intensively and found that, when olefin resin microparticles are used as the resin microparticles, the color reproducibility of the printed matter, and the storage stability and dispersion stability of the ink are improved, and the discoloration of the printed matter over time can be prevented depending on the conditions.
  • the acid value/amine value ratio represented by formula (8) shown below is preferably 0.5 ⁇ 10 ⁇ 4 to 15 ⁇ 10 ⁇ 4 , and particularly preferably 1.5 ⁇ 10 ⁇ 4 to 10 ⁇ 10 ⁇ 4 .
  • the aggregation of the yellow pigment (A) can be prevented by the interaction between the acid group present in the olefin resin microparticles and the yellow pigment (A) having an amine structure and the presence of the olefin resin microparticles around the yellow pigment (A).
  • the weight average molecular weight of the water-soluble resin is preferably in the range from 5,000 to 50,000, and more preferably in the range from 10,000 to 40,000.
  • the weight average molecular weight of the binder resin can be measured in the same manner as in the case of the pigment dispersing resin.
  • the acid value is preferably 5 to 80 mgKOH/g, and more preferably 10 to 50 mgKOH/g. If the acid value is 10 mgKOH/g or more, the blockages of the inkjet head nozzles are less likely to occur, and printing stability is remarkably improved. Further, the acid value of 80 mgKOH/g or less is preferable because the water resistance of the printed matter is good.
  • the acid value of the binder resin can also be measured in the same manner as in the case of the pigment dispersing resin.
  • the total amount of the binder resin in the yellow ink in terms of solid fraction is preferably in the range from 2 to 10% by mass, more preferably in the range from 3 to 8% by mass, and particularly preferably in the range from 3 to 6% by mass, of the total mass of the yellow ink. If the resin microparticles and the water-soluble resin are used in combination as the binder resin, the amount of the resin microparticles in the yellow ink is preferably 0.5 to 2% by mass.
  • a surfactant to the yellow ink for the purpose of adjusting the surface tension and ensuring the wettability on the recording medium.
  • all of cationic, anionic, amphoteric and nonionic surfactant can be used. Further, only one type may be used alone, or two or more types may be used in combination.
  • cationic surfactant examples include fatty acid amine salts, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts, and imidazolinium salts.
  • anionic surfactants include fatty acid soaps, N-acyl-N-methylglycine salts. N-acyl-N-methyl- ⁇ -alanine salts, N-acylglutamate salts, acylated peptides, alkyl sulfonate salts, alkyl benzene sulfonate salts, alkyl naphthalene sulfonate salts, dialkyl sulfosuccinate salts, alkyl sulfoacetate salts, ⁇ -olefin sulfonate salts, N-acyl methyl taurine, sulfated oils, higher alcohol sulfate ester salts, secondary higher alcohol sulfate ester salts, alkyl ether sulfate salts, secondary higher alcohol ethoxy sulfates, fatty acid alkylolamide sulfate ester salts, alkyl ether phosphate ester salts, and alkyl
  • amphoteric surfactant examples include carboxybetaine types, sulfobetaine types, aminocarboxylic acid salts, and imidazolinium betaine.
  • nonionic surfactant examples include polyoxyethylene secondary alcohol ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene sterol ethers, polyoxyethylene lanolin derivatives, polyoxyethylene polypropylene alkyl ethers, polyoxyethylene glycerol fatty acid esters, polyoxyethylene castor oils, hydrogenated castor oils, polyoxyethylene sorbitol fatty acid esters, polyethylene glycol fatty acid esters, fatty acid monoglycerides, polyglycerol fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, sucrose fatty acid esters, fatty acid alkanolamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, alkylamines oxides, acetylenediol-based compounds, acetylene alcohol-based compounds, polyether-modified siloxane-based compounds, and fluorine-based compounds.
  • a nonionic surfactant is preferably used in order to improve the wettability to the recording medium, and it is more preferable to select at least one selected from the group consisting of an acetylenediol-based compound, a polyether-modified siloxane-based compound, and a fluorine-based compound.
  • the yellow ink is used in the form of the ink set described below, it is preferable to use both an acetylenediol-based compound and a polyether modified siloxane-based compound together to produce a printed matter with excellent color reproducibility and other image quality for various types of recording medium.
  • the dynamic surface tension of the ink is significantly reduced by the acetylenediol-based compound to impart the wettability to various types of recording medium, and the polyether-modified siloxane-based compound can control mixing of ink droplets to improve color reproducibility and other image quality.
  • HLB Hydrophile-Lipophile Balance
  • the HLB value is one of parameters indicating hydrophilicity or hydrophobicity of the material, and the smaller the value, the higher the hydrophobicity of the material, and the larger the value, the higher the hydrophilicity of the material.
  • There are various methods for calculating the HLB value such as the Griffin method, the Davis method, and the Kawakami method, and various methods for the actual measurement are also known.
  • the HLB value is calculated using the Griffin method.
  • the Griffin method is a method in which an HLB value is obtained by formula (9) shown below using the molecular structure and molecular weight of the target material.
  • HLB value 20 ⁇ (sum of the molecular weights of hydrophilic moieties) ⁇ (molecular weight of material)
  • the HLB value of the surfactant can be obtained experimentally by the method described on p. 324 in “Surfactant Handbook” (Industrial Book Company, 1960) edited by Ichiro NISHI et al. Specifically, after dissolving 0.5 g of a surfactant in 5 mL of ethanol, the obtained solution is titrated with a 2% by mass phenol aqueous solution while stirring at 25° C. and the end point is determined as where the solution becomes turbid. When the amount of the phenol aqueous solution required up to the end point is A (mL), the HLB value can be calculated by formula (10) shown below.
  • the amount of the surfactant added to the yellow ink is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 4.0% by mass, and still more preferably 0.5 to 3.0% by mass, of the total mass of the yellow ink. If the amount is 0.1% by mass or more, the effect of sufficiently reducing the dynamic surface tension of the yellow ink can be obtained, and the image quality of the printed matter can be improved. Further, by ensuring the amount of 5.0% by mass or less, it becomes possible to control the wetting of the yellow ink and the meniscus around the inkjet head nozzles, and then the stable discharge from the inkjet heads can be achieved, and accordingly the printing stability is improved.
  • the amount of water is in the range from 45 to 95% by mass, still more preferably in the range from 50 to 75% by mass of the total mass of the yellow ink.
  • impurities such as alkali (earth) metal ions contained in the yellow ink
  • a pure water or an ion-exchanged water is preferably used as water contained in the yellow ink, instead of using general water containing various ions.
  • additives such as antifoaming agents, thickeners, preservatives, infrared absorbers, and ultraviolet absorbers can be suitably added to the yellow ink in order to obtain an ink having desired physical properties as desired.
  • addition amount of these additives 0.01 to 10% by mass or less is preferable of the total mass of the yellow ink.
  • the yellow ink preferably contains substantially no polymerizable monomer.
  • the term “contains substantially no” means that the polymerizable monomer is not intentionally added to the yellow ink, and does not exclude a small amount of contamination or generation during the production and storage of the inkjet ink.
  • the amount of the polymerizable monomer is preferably 1% by mass, and particularly preferably 0.5% by mass or less of the total mass of the yellow ink.
  • the method for producing a yellow ink is not particularly limited. From the viewpoint of obtaining an excellent printed matter and good storage stability and dispersion stability, for example, the method for producing a yellow ink preferably includes mixing a yellow pigment dispersion containing a yellow pigment (A), a basic organic compound (B), an organic solvent, and water. If the yellow ink contains an optional component, for example, the method for producing a yellow ink preferably includes mixing a yellow pigment dispersion containing a yellow pigment (A), a basic organic compound (B), an organic solvent, water, and an optional component. Examples of the optional component include, for example, a binder resin or a binder resin dispersion containing a binder resin, a surfactant, and the like.
  • the amount of the basic organic compound (B) added at the time of mixing is preferably an amount to be 0.1 to 1.0% by mass of the total mass of the yellow ink.
  • the basic organic compound (B) added at the time of mixing is preferably an alkanolamine, and more preferably triethanolamine.
  • the method for producing a yellow ink preferably includes adding to a container a yellow pigment dispersion containing a yellow pigment (A), a basic organic compound (B) in an amount to be 0.1 to 1.0% by mass of the total mass of the yellow ink, an organic solvent, water, and an optional component as desired, and mixing these components.
  • the yellow pigment dispersion may or may not contain the basic organic compound (B).
  • the pigment dispersion contains a pigment dispersing resin, water, and a yellow pigment (A), and may further contain an optional component.
  • the optional component include other pigment, a pigment derivative, an organic solvent, a base for neutralization when the pigment dispersing resin has an acid group, and the like.
  • the binder resin dispersion contains a binder resin and water, and may further contain an optional component. Examples of the optional component include an organic solvent, a base for neutralization when the binder resin has an acid group, and the like.
  • the binder resin dispersion may or may not contain the basic organic compound (B).
  • a printed matter with excellent color reproducibility can be obtained by using the yellow ink. Further, by using the yellow ink in combination with the water-based inkjet magenta ink described below, a printed matter having particularly excellent color reproducibility in the red region can be obtained.
  • a yellow ink in which a hue angle ⁇ H° measured using the following method is in the range from 70 to 105° from the viewpoint of the color reproducibility, more preferably in the range from 76 to 102°, and particularly preferably in the range from 82 to 98°.
  • standards or criteria relating to colors for example, Japan Color (Japan offset sheet-fed printing color standard), Fogra (German printing related standard).
  • SWOP US off-wheel printing standard
  • ISO 12647-2 international offset printing standards
  • the hue angle ⁇ H° of the yellow ink is measured by using a coated matter prepared by applying the yellow ink to a recording medium to form a wet film having a thickness of 6 ⁇ m and drying the wet film.
  • the yellow ink is applied using K control coater K202 manufactured by Matsuo Sangyo Co., Ltd., and the wire bar No. 1, and is then dried in an oven at 80° C. for 1 minute or more to obtain a coated matter.
  • the measurement is performed using ilPro2 manufactured by X-rite Inc. under the conditions of a light source D50, a view angle 2° and a CIE color system, and using the obtained a* and b* values.
  • UPM Finesse Gloss paper manufactured by UPM Corporation is used as a recording medium.
  • the spectral reflectance of the coated matter having a wet film thickness of 6 ⁇ m produced using the method described above is preferably 10% or less in the wavelength region of 380 to 480 nm.
  • the spectral reflectance of the printed matter is calculated using the method specified in ISO 5-3: 2009, and a StatusT Blue filter is used for measuring the yellow color.
  • the hue angle ⁇ H° can be measured using ilPro2 manufactured by X-rite Inc. in the same manner as the hue angle ⁇ H° described above.
  • the yellow ink contains a yellow pigment (A), and a pigment other than the yellow pigment (A) as desired.
  • a pigment having a hue angle ⁇ H° in the range from 82° to 98° as both of the yellow pigment (A) and the pigment other than the yellow pigment (A).
  • the pigment dispersion is diluted with water so that the pigment concentration becomes 3% by mass, and then the pigment dispersion is applied onto a recording medium in the same manner as the yellow ink coated matter having the wet film thickness of 6 ⁇ m. Then, the hue angle and the spectral reflectance of the obtained coated matter are measured using the method described above.
  • a pigment having a blue-wool scale of grade 4 or higher using the third exposure method of the “Test methods for color fastness to xenon arc lamp light” specified in JIS L 0843 as the pigment contained in the yellow ink.
  • the yellow ink according to an embodiment of the present invention it is possible to obtain a printed matter with excellent color reproducibility and light resistance which does not cause discoloration or fading over time. Further, by using an ink set obtained by combining the yellow ink with the water-based inkjet magenta ink described below (hereinafter, also simply referred to as the “magenta ink”), it is possible to obtain a printed matter having particularly excellent color reproducibility and light resistance in the red region and having a wide color gamut.
  • an ink set including a combination of the yellow ink according to an embodiment of the present invention, the magenta ink described below, the water-based inkjet cyan ink described below (hereinafter, simply referred to as the “cyan ink”) or the water-based inkjet violet ink described below (hereinafter, simply referred to as the “violet ink”) is used to obtain a printed matter having excellent color reproducibility, particularly in the red region and green region, regardless of the type of recording medium without using other water-based inkjet chromatic inks.
  • chromatic color generally refers to all colors other than colors having no chroma (black, light black (gray), and white).
  • a printed matter having a secondary color is produced by causing two or more types of inks of different colors to be contacted on a recording medium.
  • a low-absorption substrate is used as the recording medium
  • inkjet printing is performed at a high speed, or if a print ratio of the printed matter is high, the inks come into contact with each other in a wet state. In such a case, a printed matter with poor color reproducibility may be obtained depending on the inks used.
  • the yellow ink containing a yellow pigment (A) having a partial structure represented by general formula (1) is excellent in the storage stability and dispersion stability, and therefore, the dispersion state of the yellow ink is not destroyed when it comes into contact with other inks.
  • the Magenta ink contains a magenta pigment and water.
  • the magenta ink contains 1 to 10% by weight of a magenta pigment having a partial structure represented by general formula (2) shown below of the total mass of the magenta ink.
  • the magenta ink contains a magenta pigment.
  • magenta pigment examples include C. I. Pigment Red 5, 7, 12, 22, 23, 31, 48 (Ca), 48 (Mn), 49, 52, 53, 57 (Ca), 57: 1, 122, 146, 147, 150, 166, 179, 185, 202, 238, 242, 266, 269 and 282, and C. I. Pigment Violet 19, and two or more types may be used in combination.
  • the total amount of the pigment listed above in the magenta ink is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, of the total mass of the pigment contained in the magenta ink.
  • the total amount of the pigment listed above may be 100% by mass in relative to the total mass of the pigment used. That is, the ink containing the pigment listed above as a main component is preferably the magenta ink in the present description.
  • the pigment listed above may be used within the range satisfying the above conditions, and a pigment other than those listed above may be used in combination, for example, for adjusting the color.
  • the magenta ink preferably includes one or two or more selected form the group consisting of C. I. Pigment Red 48 (Ca), 48 (Mn), 122, 146, 147, 150, 185, 202, 266 and 269, and C. I. Pigment Violet 19.
  • the magenta ink preferably includes a magenta pigment having a partial structure represented by general formula (2) shown below.
  • each R 9 , R 10 and R 11 is independently any one of a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an anilide group, a carbamoyl group, a methoxycarbonyl group, an ethoxycarbonyl group, and a sulfonamide group.
  • R 2 is any one of a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, and a structure represented by general formula (3) shown below.
  • the anilide group is also referred to as a phenylaminocarbonyl group and can be represented by “—CO—NH—C 6 H 5 ”.
  • the sulfonamide group may be a substituted or unsubstituted aminosulfonyl group and can be represented by, for example, “—SO 2 —NH 2 ” or “—SO 2 —NHCH 3 ”.
  • R 13 is any one of a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an amino group, and a nitro group.
  • Each R 14 and R 15 is independently any one of a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an amino group, and a nitro group, or R 14 and R 15 are bonded to each other to form an imidazolidinone ring.
  • “*” represents a bonding site, and the structure represented by general formula (3) is bonded to a nitrogen atom in the partial structure represented by general formula (2) at the position of “*”.
  • a magenta ink including one or more selected from the group consisting of C. I. Pigment Red 146, 147, 150, 185, 266 and 269, which has one 1-phenylazo-2-naphthol structure in the molecular structure thereof, is particularly preferably selected because, when used in combination with the yellow ink according to an embodiment of the present invention, the magenta ink can suitably absorb incident light in the wavelength region where absorption by the yellow ink is small, and as a result, a printed matter with particularly excellent color reproducibility in the red region can be obtained.
  • the amount of the magenta pigment is preferably 0.1 to 10% by mass, and more preferably 1 to 9.5% by mass of the total mass of the magenta ink.
  • the magenta ink may contain, a pigment dispersing resin, a pigment derivative, an organic solvent, a binder resin, a surfactant, a basic organic compound, and other components in addition to the magenta pigment and water.
  • a pigment dispersing resin a pigment derivative
  • an organic solvent e.g., a solvent for a pigment
  • a binder resin e.g., a surfactant for a pigment that is a pigment ink.
  • surfactant e.g., sodium bicarbonate
  • the magenta ink preferably has the hue angle ⁇ Hm° of a magenta ink coated matter having a wet film thickness of 6 ⁇ m prepared in the same manner as the yellow ink of 330 to 360°.
  • the spectral reflectance of the coated matter is preferably 10% or less in the wavelength region of 480 to 580 nm.
  • a pigment having a blue-wool scale of grade 4 or higher using the third exposure method of the “Test methods for color fastness to xenon arc lamp light” specified in JIS L 0843 as the magenta pigment.
  • the hue angle ⁇ Hm° of the magenta ink coated matter having a wet film thickness of 6 ⁇ m produced in the same manner as in the case of the yellow ink is 0 to 45°.
  • the spectral reflectance of the coated matter is preferably 10% or less in the wavelength region of 480 to 580 nm.
  • the ink set may contain an ink other than the yellow ink and the magenta ink from the viewpoint of obtaining a printed matter with excellent color reproducibility.
  • the ink from the viewpoint of further enhancing the color reproducibility in the red region, it is preferable to contain an orange ink and/or a red ink in addition to the yellow ink and the magenta ink.
  • examples of the pigment contained in the orange ink include one or more selected from the group consisting of C. I. Pigment Orange 5, 13, 16, 34, 36, 38, 43, 62, 64, 67, 71 and 72, and C. I. Pigment Red 17, 49: 2, 112, 149, 178, 188 and 264.
  • C. I. Pigment Orange 43 is preferably included.
  • the amount of the pigment contained in the orange ink is preferably 0.1 to 10% by mass, and more preferably 2 to 9.5% by mass of the total mass of the orange ink.
  • magenta pigment described above is preferably contained in addition to the pigment described above. This is because the inclusion of the magenta pigment further enhances the color reproducibility of the red region.
  • the magenta pigment is preferably contained in an amount of 0.5 to 49% by mass, more preferably 1 to 45% by mass, and particularly preferably 1.5 to 40% by mass, relative to the total mass of the pigment contained in the orange ink.
  • examples of the pigment contained in the red ink include one or more selected from the group consisting of C. I. Pigment Red 177, 254 and 255, and C. I. Pigment Orange 73. Among them, form the view point of the color reproducibility and light resistance in the red region and the discharge stability, C. I. Pigment Red 254 is preferably included.
  • the amount of the pigment contained in the red ink is preferably 0.1 to 10% by mass, and more preferably 1 to 9.5% by mass of the total mass of the red ink.
  • an ink set containing a cyan ink in addition to the yellow ink and the magenta ink (and, the orange ink and/or the red ink as desired) can be preferably used.
  • the cyan ink contains a cyan pigment and water.
  • the cyan pigment contained in the cyan ink include C. I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:6, 16 and 22.
  • the total amount of the pigment listed above is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more, of the total mass of the pigment contained in the cyan ink.
  • the total amount of the pigment listed above with respect to the total mass of pigment used may be 100% by mass.
  • one or more selected from the group consisting of C. I. Pigment Blue 15:3 and C. I. Pigment Blue 15:4 are preferably included.
  • the magenta ink having the hue angle ⁇ Hm° of the coated matter of 0 to 45° from the viewpoint that a printed matter with excellent color reproducibility can be produced even with an ink set containing the chromatic ink consisting of three types of inks of the yellow ink according to an embodiment of the present invention, the magenta ink, and the cyan ink, it is preferable to use a cyan ink containing C. I. Pigment Blue 15:6.
  • the amount of the cyan pigment contained in the cyan ink is preferably 0.1 to 10% by mass, and more preferably 1 to 9.5% by mass of the total mass of the cyan ink.
  • the cyan ink may contain a pigment dispersing resin, a pigment derivative, an organic solvent, a binder resin, a surfactant, a basic organic compound, and other components in addition to the cyan pigment and water.
  • a pigment dispersing resin a pigment derivative
  • an organic solvent a binder resin
  • a surfactant a surfactant
  • a basic organic compound a surfactant that is added to the cyan pigment and water.
  • the details of these components are, for example, the same as in the case of the yellow ink described above.
  • the achromatic ink consists of at least one selected from the group consisting of a black ink, a light black (gray) ink, and a white ink.
  • an ink set containing a violet ink in addition to the yellow ink and the magenta ink (and, the orange ink and/or the red ink as desired) can be preferably used.
  • the violet ink contains a violet pigment and water.
  • the violet pigment contained in the violet ink include C. I. Pigment Violet 1, 3, 23, 27, 32, 36, 37 and 38.
  • the total amount of the pigment listed above is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more of the total mass of the pigment contained in the violet ink.
  • the total amount of the pigment listed above with respect to the total mass of pigment used may be 100% by mass.
  • the yellow ink according to an embodiment of the present invention when used in combination with the magenta ink having the hue angle ⁇ Hm° of the coated matter of 0 to 45°, from the viewpoint that the printed matter with the excellent color reproducibility can be produced even with an ink set consisting of three types of inks, one or more selected from the group consisting of C. I. Pigment Violet 3, 23, 27 and 32 are preferably included.
  • the amount of the violet pigment contained in the violet ink is preferably 0.1 to 10% by mass, and more preferably 1 to 9.5% by mass of the total mass of the violet ink.
  • the violet ink may contain a pigment dispersing resin, a pigment derivative, an organic solvent, a binder resin, a surfactant, a basic organic compound, and other components in addition to the violet pigment and water.
  • a pigment dispersing resin a pigment derivative
  • an organic solvent a binder resin
  • a surfactant a surfactant
  • a basic organic compound a surfactant that is added to the violet pigment and water.
  • the details of these components are, for example, the same as in the case of the yellow ink described above.
  • the achromatic ink consists of at least one selected from the group consisting of a black ink, a light black (gray) ink, and a white ink.
  • the cyan ink and the violet ink are distinguished by the color index name of the pigment mainly contained in the ink. That is, an ink containing C. I. Pigment Blue pigment as a main component is referred to as a cyan ink, and an ink containing C. I. Pigment Violet pigment as a main component is referred to as a violet ink. In the case of an ink containing the same amounts of C. I. Pigment Blue pigment and C. I.
  • the ink having the hue angle ⁇ Hb° of the ink coated matter having a wet film thickness of 6 ⁇ m produced in the same manner as in the case of the yellow ink of 200° or more but less than 260° is defined as a cyan ink
  • the ink having the hue angle ⁇ Hb° of 260° or more but less than 330° is defined as a violet ink.
  • the ink contains C. I. Pigment Blue pigment and/or C. I. Pigment Violet pigment as a main component, if the hue angle.
  • Hb° of the ink coated matter is less than 200°
  • the ink is regarded as a green ink described below
  • the hue angle ⁇ Hb° is 330° or more
  • the ink is regarded as a magenta ink described above.
  • the main component refers to the pigment having the largest amount based on the total mass of the pigment.
  • the ink set can be further combined with a green ink and/or a brown ink to enhance the color reproducibility in the whole color region.
  • examples of the pigment contained in the green ink include one or more selected from the group consisting of C. I. Pigment Green 7, 36 and 58.
  • a light color ink such as a light yellow ink, a light cyan ink, a light magenta ink, and a gray ink, which are inks with a low pigment concentration, can be used together depending on the applications and image quality.
  • the yellow pigment (A) used in the yellow ink is preferably used.
  • the ink set may further include a black ink.
  • a black ink By using the black ink in combination, it is possible to obtain high definition images having excellent text expression and contrast expression.
  • the pigment in the black ink examples include an organic pigment such as aniline black, Lumogen black and azomethine black, and an inorganic pigment such as a carbon black and iron oxide.
  • an organic pigment such as aniline black, Lumogen black and azomethine black
  • an inorganic pigment such as a carbon black and iron oxide.
  • a plurality of color pigments such as a yellow pigment, a magenta pigment, and a cyan pigment may be used as the composite black.
  • the carbon black pigment a carbon black produced using the furnace method or the channel method is preferable.
  • these carbon blacks those having characteristics such as a primary particle size of 11 to 40 m ⁇ m (nm), a specific surface area by the BET method of 50 to 400 m 2 /g, a volatile fraction of 0.5 to 10% by mass, and a pH value of 2 to 10 are preferable.
  • Examples of commercially available products having such characteristics include No.
  • the amount of the pigment contained in the black ink is preferably 0.1 to 10% by mass, and more preferably 1 to 9.5% by mass of the total mass of the black ink.
  • the ink set can include a white ink.
  • a white ink By using the white ink in combination, a printed matter with good legibility can be formed on a transparent recording medium or a recording medium having low brightness.
  • the yellow ink when used in combination with the yellow ink according to an embodiment of the present invention, it is possible to obtain a clear and high definition printed matter on the recording medium described above as well as when recording on a white medium.
  • the pigment that can be used for the white ink include an inorganic white pigment and an organic white pigment.
  • examples of the inorganic white pigment include alkaline earth metal sulfates such as barium sulfate, alkaline earth metal carbonates such as calcium carbonate, silica such as fine powder silicic acid and synthetic silicates, calcium silicate, alumina, alumina hydrate, titanium oxide, zinc oxide, talc, clay and the like. Titanium oxide is most preferable from the viewpoint of hiding power and coloring power.
  • the average particle size of the white pigment is preferably 50 to 500 nm. By ensuring the average particle size within the range described above, it is possible to achieve all of the hiding property, storage stability, and discharge stability.
  • the size is more preferably 100 to 400 nm.
  • the amount of the pigment contained in the white ink is preferably 3 to 50% by mass, and more preferably 5 to 30% by mass of the total mass of the white ink.
  • the yellow ink or the ink set according to an embodiment of the present invention is printed on a recording medium by the inkjet printing system.
  • the inkjet printing system both a single-pass system in which the inkjet ink is discharged to a recording medium only once for recording, and a serial method in which discharge and recording are performed while reciprocally scanning a short shuttle head in a direction perpendicular to the conveyance direction of the recording medium may be adopted.
  • the system of discharging the ink there are no particular limitations on the system of discharging the ink, and it is possible to use all known systems such as, for example, a charge control system of discharging the ink by using an electrostatic attraction force; a drop on demand system (a pressure pulse system) using vibration pressure of the piezo element; an acoustic inkjet system of changing an electric signal into an acoustic beam and irradiating the ink to discharge the ink using radiation pressure; and a thermal inkjet (bubble Jet [registered trademark]) system of heating the ink to form bubbles and using the generated pressure.
  • the inkjet heads used for discharging the ink may be both an on-demand system and a continuous system.
  • the amount of ink droplets discharged from the inkjet head is preferably 0.2 to 50 picoliter, and more preferably 1 to 30 picoliter.
  • An inkjet recording apparatus mounted with the inkjet heads preferably further includes an ink drying mechanism.
  • the drying method used in the drying mechanism includes a heated drying method, a hot air drying method, an infrared ray (for example, infrared light with a wavelength of 700 to 2,500 nm) drying method, a microwave drying method, and a drum drying method.
  • the drying temperature is preferably 35 to 100° C.
  • the hot air temperature is preferably 50 to 250° C.
  • the drying method may be used alone, or a plurality of drying methods may be used in succession, or may be used in combination at the same time. For example, by using the heated drying method and the hot air drying method together, the ink can be dried more quickly than when each of them is used alone.
  • the recording medium on which the yellow ink or the ink set is printed is not particularly limited.
  • a paper substrate such as a high-quality paper, a coated paper, an art paper, a cast paper, and a synthetic paper
  • a plastic substrate such as polycarbonate, hard vinyl chloride, soft vinyl chloride, polystyrene, foamed styrol, PMMA, polypropylene, polyethylene, and PET
  • a metal substrate such as stainless steel; glass; and wood can be used.
  • the yellow ink or the ink set can be suitably used not only on a high-absorption substrate such as an inkjet paper or a high-quality paper which have an absorbent layer, but also on a low-absorption substrate such as a coated paper, an art paper, and a vinyl chloride sheet which are commonly used in industrial applications.
  • a high-absorption substrate such as an inkjet paper or a high-quality paper which have an absorbent layer
  • a low-absorption substrate such as a coated paper, an art paper, and a vinyl chloride sheet which are commonly used in industrial applications.
  • the yellow pigments used in the examples are as shown below.
  • the measurement method of the amount of the solid fraction was as follows. A portion of the supernatant was added to an aluminum container whose mass had been previously measured (the mass is W1), and the total mass was measured (the total mass is W2). Then, the aluminum container was left at a temperature of 80° C. until the liquid component was completely evaporated, and then the total mass was measured again (the total mass is W3). The amount of the solid fraction was calculated by the formula: 95 ⁇ [(W3 ⁇ W1)+(W2 ⁇ W1)].
  • Yellow pigment dispersions 2 to 11 were produced in the same manner as in the yellow pigment dispersion 1 except that the types of pigments were changed to those shown in Table 1.
  • Table 1 also describes the amount of the impurities in the pigments measured using the method described above.
  • An aqueous dispersion of an olefin resin microparticles 2 (non-volatile fraction: 30% by mass) was produced in the same manner as in the aqueous dispersion of the olefin resin microparticles 1 except that the acid group-containing polyolefin was changed to a oxidized polyethylene wax having an acid value of 41 mgKOH/g and a melting point of about 140° C., the amount added of the polyethylene wax was 32 parts, the amount added of the acid group-containing polyolefin was 58 parts, and the amount added of dimethylaminoethanol was 2.3 parts.
  • an aqueous dispersion of an olefin resin microparticles 3 (non-volatile fraction: 30% by mass) was produced in the same manner as in the aqueous dispersion of the olefin resin microparticles 2 except that the acid group-containing polyolefin was changed to an acid-modified polyethylene wax having an acid value of 60 mgKOH/g and a melting point of about 105° C. and the amount added of dimethylaminoethanol was 3.4 parts.
  • Each of the yellow pigment dispersions obtained above, a binder resin (JE-1056 (solid fraction: 42.5%, particle size: 50 nm), resin microparticles manufactured by SEIKO PMC CORPORATION), a solvent, a surfactant (Surfynol 104E, an acetylenediol-based compound manufactured by Nissin Chemical Industry Co., Ltd.), a basic organic compound (B) (diethanolamine (pKa 8.9)), and water were added while stirring to a mixing container equipped with a stirrer and mixed for 1 hour so as to have the composition shown in Table 2.
  • a binder resin JE-1056 (solid fraction: 42.5%, particle size: 50 nm), resin microparticles manufactured by SEIKO PMC CORPORATION
  • a solvent a solvent
  • a surfactant Surfynol 104E, an acetylenediol-based compound manufactured by Nissin Chemical Industry Co., Ltd.
  • B basic organic
  • the amount of JE-1056 shown in the table is the amount of the solid fraction.
  • Each of the water-based yellow inks 1 to 13 obtained above was applied on UPM Finesse Gloss paper manufactured by UPM Corporation. and coating was performed by using K control coater K202 manufactured by Matsuo Sangyo Co., Ltd., and wire bar No. 1 (wet thickness of coating: 6 ⁇ m), and then dried in an oven at 80° C. for 1 minute or more to produce a coated matter.
  • the obtained yellow ink coated matters were evaluated for the hue, image density (OD values), spectral reflectance, and light resistance shown below.
  • the hue and image density of each of the yellow ink coated matters obtained above were measured using ilPro2 manufactured by X-Rite Inc. under the conditions of a light source D50, a view angle 2°, and a CIE color system.
  • the chroma C and the hue angle ⁇ H° were calculated from the obtained a* and b*.
  • the chroma C was calculated using formula (11) shown below, and the hue angle ⁇ H° was calculated using the formula described above.
  • the chroma C is a practically usable level if it is 70 or more, a preferable level for practical use if it is 85 or more, and a particularly preferable level for practical use if it is 95 or more.
  • the hue angle ⁇ H° is a practically usable level if it is 70 to 105°, a preferable level for practical use if it is 76 to 102°, and a particularly preferable level for practical use if it is 82 to 98°.
  • the image density (OD value) is desirably 0.65 or more, preferably 1.0 or more, and particularly preferably 1.1 or more.
  • the spectral reflectance in the wavelength region of 380 to 480 nm of each of the yellow ink coated matters obtained above was measured in every 10 nm using ilPro2 manufactured by X-Rite Inc. under the conditions of a light source D50, a view angle 2°, and a CIE color system. As described above, it is preferable that the spectral reflectance is 10% or less in the entire wavelength region described above.
  • the light resistance test was conducted using the yellow ink coated matters obtained above and 2 to 7 grade standard blue dyed fabrics (blue scales) specified in JIS L 0841: 2004, in accordance with the third exposure method specified in JIS L 0843: 2006 “Test methods for color fastness to xenon arc lamp light”, using a xenon weather meter SX 75 manufactured by Suga Test Instruments Co., Ltd. under the conditions of irradiance 60 W, a black panel temperature 63° C., and 50% RH.
  • the light resistance of the yellow ink coated matter was determined by grade by visually determining the degree of fading when the blue scale of each grades faded. The results are shown in Table 2, and grade 3 and above was determined as a practically usable level, and grade 6 and above was determined as a preferable level for practical use.
  • the water-based yellow inks 1 to 13 After measuring the viscosity of the water-based yellow inks 1 to 13 by using an E-type viscometer (TVE25L-type viscometer manufactured by Toki Sangyo Co., Ltd.), the water-based yellow inks 1 to 13 were store in an oven at 70° C. Then, the water-based yellow inks were taken out every day, the viscosity was measured again using the same method as described above, and the range of change of the viscosity was confirmed to evaluate the storage stability.
  • the evaluation criteria were as follows, and evaluations of A, B, and C were determined as a practically usable level.
  • the water-based yellow inks 1 to 13 were stored in an oven at 70° C. for 2 weeks to prepare time elapsed yellow inks 1 to 13. Then, coated matters (wet film thickness: 6 ⁇ m) of the time elapsed yellow inks 1 to 13 were prepared in the same manner as in the yellow ink coated matters described above, and the hue change was evaluated by visually comparing with the yellow ink coated matters 1 to 13 which had not been time elapsed.
  • the evaluation criteria were as follows, and evaluation of A was determined as a practically usable level.
  • the chroma C and the hue angle ⁇ H° defined in the CIELAB color space were at least a practically usable level or higher, the light resistance was 3 grade or more, and the evaluation results regarding the storage stability and the hue change of the time elapsed yellow ink were also at a practically usable level.
  • C. I. Pigment Yellow 139 and 185 which were used in the yellow inks 4 to 7 (Examples 4 to 7) had the chroma C and the hue angle ⁇ H° at a preferable level for practical use, had a high image density (OD value), and also had a spectral reflectance in the 380 to 480 nm wavelength region of 10% or less.
  • C. I. Pigment Yellow 139 and 185 therefore can produce a high concentration yellow ink having extremely high image density in addition to the color reproducibility and light resistance.
  • the yellow inks 5 and 6 (Examples 5 and 6) used the same C. I. Pigment Yellow 185, a difference in the image density was found. It is considered that the pigment used in the yellow ink 6 had the amount of impurities of 5% by mass or less, so that foaming and/or inhibition of the adsorption of the pigment dispersing resin could be suppressed during dispersion.
  • C. I. Pigment Yellow 12 and 14 used in the yellow inks 8 and 9 are yellow pigments generally used in offset printing and gravure printing. If these pigments are used, the chroma C and the hue angle ⁇ H° defined in the CIELAB color space are a particularly preferable level for practical use, and the spectral reflectance in the wavelength region of 380 to 480 nm can be suppressed to 10% or less, and therefore it is possible to produce a high concentration yellow ink.
  • the light resistance is as low as grade 2, and in the ink 8, the evaluation results regarding the storage stability and the hue change of the time elapsed yellow ink were also at a problematic level for practical use.
  • the pigment used in the yellow inks 10 and 11 (Comparative Examples 3 and 4) is a yellow ink which had a poor evaluation result regarding the hue change of the time elapsed yellow ink and was able to cause discoloration and fading over time.
  • the yellow ink 13 (Comparative Example 6) was an ink having a boiling point of 240° C. or higher and the amount of the organic solvent of more than 5% by mass, and it was confirmed that the hue change of the time elapsed yellow ink was inferior to the yellow inks 6 and 7 (Examples 6 and 7) using the same pigment.
  • the yellow inks 14 to 34 having the composition shown in Table 3 were produced in the same manner as in the water-based yellow ink 1 to 13. Next, the yellow inks 14 to 34 obtained were subjected to the storage stability test using the method described above. Further, after preparing yellow ink coated matters (wet film thickness: 6 ⁇ m) using the method described above, the light resistance was evaluated using the method described above. The evaluation results of the storage stability and the light resistance of the yellow inks 14 to 34 are as shown in Table 3.
  • the types and the pKa value at 25° C. of the basic organic compounds used in Table 3 are as follows.
  • the yellow inks 22 to 31 were evaluated for the tendency when the amount of triethanolamine used as the basic organic compound (B) was changed.
  • C. I. Pigment Yellow 139 and 185 used for evaluation by ensuring the amount of 0.1 to 1% of the total mass of the yellow ink, it was possible to achieve both the light resistance and storage stability.
  • yellow inks 35 to 58 having the compositions shown in Table 4 were produced in the same manner as in the water-based yellow inks 1 to 13.
  • the storage stability of the obtained yellow inks 35 to 58 was evaluated using the method described above.
  • the color difference ⁇ E was evaluated using the method described below.
  • the evaluation results of the storage stability and the color difference ⁇ E of the yellow inks 35 to 58 are as shown in Table 4.
  • a plurality of yellow ink coated matters having different recording media were prepared for each of the water-based yellow inks 35 to 58 obtained above in the same manner as in the method for preparing the yellow ink coated matter described above except for using the recording media shown below.
  • the hue (L* value, a* value, and b* value) was measured using ilPro2 manufactured by X-Rite Inc. under the conditions of a light source D50, a view angle 2°, and a CIE color system.
  • the color difference ⁇ E was calculated for each of the water-based yellow ink 35 to 58 for all combinations of the yellow ink coated matters, and the maximum value of the color difference ⁇ E was compared to evaluate the difference in hues of the yellow ink coated matters caused by the different recording media.
  • the evaluation criteria were as follows, and evaluations of A. B, and C were determined as a practically usable level.
  • yellow inks such as yellow inks 38, 40 and 42 to 43, which contained two or more types selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol as the water-soluble organic solvent, and had a total amount thereof of 10 to 30% by mass of the total mass of the yellow ink has a small color difference ⁇ E and excellent storage stability even if any recording medium is used.
  • the yellow inks 43, 45 to 48 and the yellow inks 49 to 52 were evaluated by changing an HLB value of the surfactant.
  • HLB value 8 or less, particularly preferably 6 or less
  • the yellow inks 53 to 56 were evaluated for the influence on the quality of the yellow ink when the olefin resin microparticles were used as the binder resin.
  • the acid value/amine value ratio represented by formula (8) above was 0.53 ⁇ 10 ⁇ 4 , 1.6 ⁇ 10 ⁇ 4 , 9.9 ⁇ 10 ⁇ 4 , or 14.5 ⁇ 10 ⁇ 4 , respectively.
  • the storage stability was improved in the yellow inks 54 and 55 in which the acid value/amine value ratio were 1.5 ⁇ 10 ⁇ 4 to 10 ⁇ 10 ⁇ 4 .
  • an ink set composed of a yellow ink and a magenta ink was prepared, and the chroma Cm, the image density (OD value), and the spectral reflectance in the wavelength region of 380 to 480 nm were evaluated.
  • Yellow inks 59 to 63 having the compositions shown in Table 5 were produced in the same manner as in the water-based yellow inks 1 to 13.
  • magenta pigment dispersion 1 10 parts of propylene glycol, 10 parts of 1,2-butanediol, 9 parts of JE-1056 (solid fraction: 42.5%, particle size: 50 nm) which is a resin emulsion manufactured by SEIKO PMC CORPORATION, 1 part of Surfynol 104E, and 54 parts of water were added while stirring, and mixed for 1 hour. Then, filtration was carried out with a membrane filter with a pore size of 1 ⁇ m to remove coarse particles to obtain a magenta ink 1.
  • magenta pigment dispersions 2 to 8 were produced in the same manner as in the magenta pigment dispersion 1 except that the types of pigments were changed as shown in Table 6. Then, the magenta inks 2 to 8 was produced in the same manner as in the magenta ink 1 except that the magenta pigment dispersion 1 was changed to the magenta pigment dispersions 2 to 8.
  • magenta inks and the yellow inks obtained above were combined as shown in Table 7, and coated matters (red coated matters) were produced using the method described below.
  • each of the magenta inks 1 to 8 obtained above was applied on UPM Finesse Gloss paper manufactured by UPM Corporation, and coating was performed by using K control coater K202 manufactured by Matsuo Sangyo Co., Ltd., and wire bar No. 1 (wet thickness of coating: 6 ⁇ m), and then dried in an oven at 80° C. for 1 minute or more to produce magenta ink coated matters.
  • the yellow inks 59 to 60 were applied so as to overlap the magenta ink coating film and to form the combinations described in Table 4.
  • the apparatus used for coating was the same as that used for the production of the magenta ink coated matters. After coating, the coated matters were dried in an oven at 80° C. for 1 min or more to produce coated matters (red coated matters) in which the magenta ink and the yellow ink were layered.
  • the hue angle ⁇ Hm° of each of the magenta ink coated matters obtained above was measured using the same manner as in the yellow ink coated matter, and the hue angle ⁇ Hm° of the coated matter formed using each of the magenta ink 1, 3 or 8 was 330 to 360°, and the hue angle ⁇ Hm° of the coated matter formed using each of the magenta ink 2, 4, 5 or 7 was 0 to 45°.
  • the hue and the image density of each of the red coated matters obtained above was measured using ilPro2 manufactured by X-Rite Inc. under conditions of a light source D50, a view angle 2°, and a CIE color system.
  • the chroma of the red coated matter (referred to as Cm) was calculated from the obtained a* and b* by using formula (11) described above.
  • the obtained chroma Cm was compared with the chroma of the red standard color in Japan Color 2007 and Fogra 39 (hereinafter referred to as C STD ) to evaluate the color reproducibility of the red coated matter.
  • the evaluation criteria for the chroma C were as follows, and evaluations of A and B were determined as a practically usable level.
  • the image density (OD value) is preferably 1.2 or more, and particularly preferably 1.4 or more.
  • the spectral reflectance in the wavelength region of 380 to 480 nm of each of the red coated matters obtained by the same method as in Evaluation 2 above was measured in every 10 nm. It is preferable that the spectral reflectance is 5% or less in the entire wavelength region above from the viewpoint of the color reproducibility.
  • the quinacridone pigment used in the magenta ink above has reflection in the wavelength region of 380 to 480 nm, the red color reproduction region overlayered with the yellow ink tends to be narrowed.
  • the yellow ink according to an embodiment of the present invention as described above, a printed matter having excellent color reproducibility in the red region and image density can be obtained.
  • the yellow ink according to an embodiment of the present invention is combined with a magenta ink containing a magenta pigment having a partial structure represented by general formula (2), a printed matter with excellent color reproducibility and high image density was able to be obtained as in the case of the magenta ink containing the quinacridone pigment.
  • cyan inks and violet inks were further produced and combined with the yellow inks and the magenta inks obtained above to evaluate the hue of color patch printed matters.
  • cyan pigment dispersion 1 10 parts of propylene glycol, 10 parts of 1,2-butanediol, 9 parts of JE-1056 (solid fraction: 42.5%, particle size: 50 nm) which is a resin emulsion manufactured by SEIKO PMC CORPORATION, 1 part of Surfynol 104E, 0.8 parts of triethanolamine, and 54.2 parts of water were added while stirring, and mixed for 1 hour. Then, filtration was carried out with a membrane filter having a pore size of 1 ⁇ m to remove coarse particles to obtain a cyan ink 1.
  • Cyan pigment dispersion 2 and violet pigment dispersions 1 to 4 were produced in the same manner as in the cyan pigment dispersion 1 except that the types of pigments were changed as shown in Table 8. Then, cyan inks 1 to 3 and violet inks 1 to 4 having the compositions shown in Table 9 were produced.
  • An inkjet discharge apparatus having four ink-jet heads (model: KJ4B-1200, design resolution: 600 dpi) manufactured by Kyocera Corporation on an upper part of a conveyor capable of conveying a substrate was prepared, the combinations of inks shown in Table 10 were used as an ink set, and the inks were filled from an upstream side so as to become a violet ink, a cyan ink, a magenta ink, and a yellow ink.
  • Example 53 54 55 56 57 58 59 Ink Inks Yellow No. 59 59 59 60 60 60 60 set contained ink Pigment P.Y.139 P.Y.139 P.Y.139 P.Y.185 P.Y.185 P.Y.185 P.Y.185 in Ink Magenta No. 4 4 4 5 5 5 5 set ink Pigment P.R.150 P.R.150 P.R.150 P.R.185 P.R.185 P.R.185 P.R.185 P.R.185 Cyan No. 1 2 3 ink Pigment P.B.15:6 P.B.15:3 + P.B.15:3 + P.B.15:6 P.B.15:6 Violet No.
  • the hue of each of the color patch printed matters obtained above was measured using ilPro2 manufactured by X-Rite Inc. under the conditions of a light source D50, a view angle 2°, and a CIE color system.
  • the chroma Cc and the hue angle ⁇ Hm° of each color patch printed matter were calculated from the obtained a* and b*.
  • the chroma Cc was calculated using formula (11) described above and the hue angle ⁇ Hm° was calculated using the formula described above.
  • the hue angle ⁇ Hc° of each color patch was compared with the hue angle of each of the following standard colors, and the chroma Cc of the color patch having the smallest difference thereof was compared with the chroma of the standard color to evaluate the hue of color patch printed matter. In the three standard colors except for Warm-Red, evaluation of A was determined as a practically usable level.
  • the chroma Cc of the color patch having the smallest difference from the hue angle of the standard color was equal to or higher than the chroma of the standard color.
  • the magenta ink contains a magenta pigment having a partial structure represented by general formula (2)
  • the cyan ink contains one type selected from the group consisting of C. I. Pigment Blue 15:3 and 15:6
  • the violet ink contains one type selected from the group consisting of C. I.
  • magenta inks 3 and 8 which contain a magenta pigment having the structure of general formula (2) and a hue angle ⁇ Hm° of the coated matter of 330 to 360°, have particularly excellent color reproducibility in the red region.
  • magenta inks 2, 4, 5, and 7 which contain a magenta pigment having the structure of general formula (2) and hue angle ⁇ Hm° of the coated matter of 0 to 45°, have excellent overall color reproducibility (CMY or RGB).

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